The present invention pertains to a technical field of a seat weight measuring apparatus for measuring the weight of a seat for a vehicle such as an automobile including load applied to the seat.
As a seat weight measuring apparatus, there has been conventionally proposed a seat weight measuring apparatus comprising a force input member to which force due to the weight of a seat for a vehicle such as an automobile including load applied to the seat is applied and which transmits the force to a sensor portion such as, for example, Japanese Patent Publication No. 2000-258234 (hereby incorporated by reference herein in its entirety).
As shown in FIGS. 5(A) and 5(B), a seat weight measuring apparatus 100 disclosed in Japanese Patent Publication No. 2000-2582341 has a pin bracket 101 as the force input member. As force due to the seat weight is applied to the pin bracket 101, the pin bracket 101 transmits this force to a sensor plate 104 of a sensor portion 103 through an arm 102. Thus, the sensor plate 104 is distorted. The distortion is detected by a strain gauge (not shown) mounted on the sensor plate 104, thereby measuring the seat weight of the vehicle seat on which the occupant sits.
By the way, as shown in FIGS. 6(A) through 6(D), in the seat weight measuring apparatus 100, a stopper bolt 105 extends through holes 106 of left and right side walls 101L, 101R of the pin bracket 101 and also extends through elongate holes 108, which are elongate in the vertical direction, formed in left and right side walls 107L, 107R of the base frame 107 and through holes 109 formed in side walls 102L, 102R of the arm 102. The arm 102 is pivotally supported to the side walls 107L, 107R of the base frame 107 by a pivot bolt 110.
As shown in FIG. 6(A), as vertical force F is applied to the pin bracket 101 in the normal state, the stopper bolt 105 most always moves within the elongate holes 108 because the force F is in a normal level so that the force F is seldom or never transmitted to the side walls 107A of the base frame 107. Even when the stopper bolt 105 collides with upper or lower edges of the inner peripheries of the elongate holes 108, force acting on the side walls 107A of the base frame 107 is small because the force F is in a normal level. By the vertical movement of the stopper bolt 105, the arm 102 pivots about the pivot bolt 105 so that the force F (that is, the seat weight) is detected by the sensor portion.
In the event of a vehicle collision or the like, a large load is generated on the vehicle seat so that large force F is applied upwardly to the pin bracket 101. To withstand the large force F, the pin bracket 101 is required to have enough large strength. That is, as shown in FIG. 6(B), when such large force F significantly larger than that in the normal state is applied upwardly to the pin bracket 101, the stopper bolt 105 widely moves upwardly so as to collide with the upper edges of the inner peripheries of the elongate holes 108, thereby pressing the side walls 107A of the base frame 107. Because of the reaction force, the stopper bolt 105 presses the side walls 101A of the pin bracket 101. Accordingly, large stress is generated at portions α lower than the holes 106 of the side walls 101A of the pin bracket 101. Therefore, the portions of the side walls 101A of the pin bracket 101 are required to have large strength to withstand to the stress.
To increase the strength of the portions α of the side walls 101A, it can be considered to increase the vertical length of the portions from the holes 106 to the lower edges of the side walls 101A of the pin bracket 101 or increase the thickness of the side walls 101A.
However, the increase in length of the portions α of the side walls 101A increases the height of the pin bracket 101 and the increase in thickness of the side walls 101A increases the weight and the width of the pin bracket 101. The increase in size of the seat weight measuring apparatus 100 leads to restriction on the layout, thus causing a problem of reducing the degree of installation freedom.
As another way of coping with large stress produced on the portions α lower than the holes 106 of the side walls 101A of the pin bracket 101, it can be considered to provide a force bearing member such as a bolt exclusively for bearing the force, wherein the force bearing member penetrates the wide walls 107A of the base frame 107 and the side walls 101A of the pin bracket 101 to bear the force. Therefore, the large force F applied to the pin bracket 101 is shared and borne by the stopper bolt 105 and the force bearing member, thereby reducing the stress developed on the portions α of the side walls 101A.
However, the way of providing the force bearing member for single purpose also has problems not only increasing the number of parts but also increasing the entire length of the base frame 107.
The present invention was made for under the aforementioned circumstances and an object of the present invention is to provide a seat weight measuring apparatus capable of further securely withstanding large force due to large load, such as force in the event of a vehicle collision, applied to a vehicle seat, without increase in number of parts and increase in size of the apparatus.